One type of vehicle safety system is an occupant protection system. The protection system includes one or more sensor devices for sensing vehicle characteristics and/or occupant characteristics. The sensed characteristics are used to determine whether a vehicle occupant needs to be protected (e.g., restrained) and/or determine a deployment profile of a device that accomplishes a protection function. Examples of the sensor devices include a vehicle acceleration sensor, an occupant position sensor, and an occupant weight sensor.
The system includes one or more actuatable protection devices for protecting (e.g., restraining) the occupant. Examples of such protection devices include an air bag module, a knee bolster module, and a seat belt pretensioner module.
As the sophistication of occupant protection systems has increased, the number and complexity of the sensor and protection devices in a single vehicle has increased. In response to the increased number and complexity of devices, there has been a movement toward centralized control of the devices to reduce cost and to increase reliability of the overall protection system. In order to accomplish the centralized control, a bus architecture is used for conveyance of communication signals. A potential exists that bus communication may be interrupted by such occurrences as crushing during a vehicle collision and associated deployment actuation of the protection devices within the system during the collision.
One type of protection system that has been developed utilizing centralized control and communication via a bus is a daisy chain topology system. Within the daisy chain system, at least one conductor of the communication bus extends through each successive device. Daisy chain topology has an advantage in that individual remote devices (e.g., sensor and protection devices) can be installed into the associated vehicle in a non-programmed state (e.g., unaddressed). Once the devices are installed, a central control unit (CCU) programs each device via sequential polling or the like. Thus, it is desirable to maintain an ability to have a CCU program devices.